Linux C Read GPS data from UART
1.使用Terminal終端機介面(TTY)，讓Linux系統透過UART串列埠連接GPS。終端機介面有二種模式：正規(canonical)模式和非正規(non-canonical=raw input)模式。
模式 說明
- 正規(canonical)模式: 終端設備會處理特殊字元，且會以一次一列的方式將輸入傳給應用程式。
正規模式
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原文
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Canonical Input
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Canonical input is line-oriented. Input characters are put into a buffer which can be edited interactively by the user until a CR (carriage return) or LF (line feed) character is received.
When selecting this mode you normally select the ICANON, ECHO, and ECHOE options:
options.c_lflag |= (ICANON | ECHO | ECHOE); |
- 非正規(non-canonical)模式:又稱為raw模式。在這種模式中，終端設備不會處理特殊字元，且會以一次一個字元的方式將輸入傳給應用程式。
非正規
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原文
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Raw Input
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Raw input is unprocessed. Input characters are passed through exactly as they are received, when they are received. Generally you'll deselect the ICANON, ECHO, ECHOE, and ISIG options when using raw input:
options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG); |
2.開啟通訊埠
#include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <termios.h> #include <stdio.h> #define MODEMDEVICE "/dev/ttyS2" ... fd = open(MODEMDEVICE, O_RDWR|O_NOCTTY|O_NDELAY );
if (fd <0) {perror(MODEMDEVICE); exit(-1); }
... |
| struct termios{ tcflag_t c_iflag; /*輸入模式*/ tcflag_t c_oflag; /*輸出模式*/ tcflag_t c_cflag; /*控制模式*/ tcflag_t c_lflag; /*局部模式*/ cc_t c_cc[NCCS]; /*特殊控制字元*/ } |
| Constant | Description |
|---|---|
| INPCK | Enable parity check |
| IGNPAR | Ignore parity errors |
| PARMRK | Mark parity errors |
| ISTRIP | Strip parity bits |
| IXON | Enable software flow control (outgoing) |
| IXOFF | Enable software flow control (incoming) |
| IXANY | Allow any character to start flow again |
| IGNBRK | Ignore break condition |
| BRKINT | Send a SIGINT when a break condition is detected |
| INLCR | Map NL to CR |
| IGNCR | Ignore CR |
| ICRNL | Map CR to NL |
| IUCLC | Map uppercase to lowercase |
| IMAXBEL | Echo BEL on input line too long |
| Constant | Description |
|---|---|
| OPOST | Postprocess output (not set = raw output) |
| OLCUC | Map lowercase to uppercase |
| ONLCR | Map NL to CR-NL |
| OCRNL | Map CR to NL |
| NOCR | No CR output at column 0 |
| ONLRET | NL performs CR function |
| OFILL | Use fill characters for delay |
| OFDEL | Fill character is DEL |
| NLDLY | Mask for delay time needed between lines |
| NL0 | No delay for NLs |
| NL1 | Delay further output after newline for 100 milliseconds |
| CRDLY | Mask for delay time needed to return carriage to left column |
| CR0 | No delay for CRs |
| CR1 | Delay after CRs depending on current column position |
| CR2 | Delay 100 milliseconds after sending CRs |
| CR3 | Delay 150 milliseconds after sending CRs |
| TABDLY | Mask for delay time needed after TABs |
| TAB0 | No delay for TABs |
| TAB1 | Delay after TABs depending on current column position |
| TAB2 | Delay 100 milliseconds after sending TABs |
| TAB3 | Expand TAB characters to spaces |
| BSDLY | Mask for delay time needed after BSs |
| BS0 | No delay for BSs |
| BS1 | Delay 50 milliseconds after sending BSs |
| VTDLY | Mask for delay time needed after VTs |
| VT0 | No delay for VTs |
| VT1 | Delay 2 seconds after sending VTs |
| FFDLY | Mask for delay time needed after FFs |
| FF0 | No delay for FFs |
| FF1 | Delay 2 seconds after sending FFs |
| Constant | Description | Key |
|---|---|---|
| VINTR | Interrupt | CTRL-C |
| VQUIT | Quit | CTRL-Z |
| VERASE | Erase | Backspace (BS) |
| VKILL | Kill-line | CTRL-U |
| VEOF | End-of-file | CTRL-D |
| VEOL | End-of-line | Carriage return (CR) |
| VEOL2 | Second end-of-line | Line feed (LF) |
| VMIN | Minimum number of characters to read | |
| VTIME | Time to wait for data (tenths of seconds) |
4.範例
Canonical Input Processing
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <stdio.h>
/* baudrate settings are defined in <asm/termbits.h>, which is
included by <termios.h> */
#define BAUDRATE B38400
/* change this definition for the correct port */
#define MODEMDEVICE "/dev/ttyS2"
#define _POSIX_SOURCE 1 /* POSIX compliant source */
#define FALSE 0
#define TRUE 1
volatile int STOP=FALSE;
int main(int argc, char *argv[])
{
int fd,c, res;
struct termios oldtio,newtio;
char buf[255];
/*
Open modem device for reading and writing and not as controlling tty
because we don't want to get killed if linenoise sends CTRL-C.
*/
fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY );
if (fd <0) {perror(MODEMDEVICE); exit(-1); }
tcgetattr(fd,&oldtio); /* save current serial port settings */
bzero(&newtio, sizeof(newtio)); /* clear struct for new port settings */
/*
BAUDRATE: Set bps rate. You could also use cfsetispeed and cfsetospeed.
CRTSCTS : output hardware flow control (only used if the cable has
all necessary lines. See sect. 7 of Serial-HOWTO)
CS8 : 8n1 (8bit,no parity,1 stopbit)
CLOCAL : local connection, no modem contol
CREAD : enable receiving characters
*/
newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
/*
IGNPAR : ignore bytes with parity errors
ICRNL : map CR to NL (otherwise a CR input on the other computer
will not terminate input)
otherwise make device raw (no other input processing)
*/
newtio.c_iflag = IGNPAR | ICRNL;
/*
Raw output.
*/
newtio.c_oflag = 0;
/*
ICANON : enable canonical input
disable all echo functionality, and don't send signals to calling program
*/
newtio.c_lflag = ICANON;
/*
initialize all control characters
default values can be found in /usr/include/termios.h, and are given
in the comments, but we don't need them here
*/
newtio.c_cc[VINTR] = 0; /* Ctrl-c */
newtio.c_cc[VQUIT] = 0; /* Ctrl-\ */
newtio.c_cc[VERASE] = 0; /* del */
newtio.c_cc[VKILL] = 0; /* @ */
newtio.c_cc[VEOF] = 4; /* Ctrl-d */
newtio.c_cc[VTIME] = 0; /* inter-character timer unused */
newtio.c_cc[VMIN] = 1; /* blocking read until 1 character arrives */
newtio.c_cc[VSWTC] = 0; /* '\0' */
newtio.c_cc[VSTART] = 0; /* Ctrl-q */
newtio.c_cc[VSTOP] = 0; /* Ctrl-s */
newtio.c_cc[VSUSP] = 0; /* Ctrl-z */
newtio.c_cc[VEOL] = 0; /* '\0' */
newtio.c_cc[VREPRINT] = 0; /* Ctrl-r */
newtio.c_cc[VDISCARD] = 0; /* Ctrl-u */
newtio.c_cc[VWERASE] = 0; /* Ctrl-w */
newtio.c_cc[VLNEXT] = 0; /* Ctrl-v */
newtio.c_cc[VEOL2] = 0; /* '\0' */
/*
now clean the modem line and activate the settings for the port
*/
tcflush(fd, TCIFLUSH);
tcsetattr(fd,TCSANOW,&newtio);
/*
terminal settings done, now handle input
In this example, inputting a 'z' at the beginning of a line will
exit the program.
*/
while (STOP==FALSE) { /* loop until we have a terminating condition */
/* read blocks program execution until a line terminating character is
input, even if more than 255 chars are input. If the number
of characters read is smaller than the number of chars available,
subsequent reads will return the remaining chars. res will be set
to the actual number of characters actually read */
res = read(fd,buf,255);
buf[res]=0; /* set end of string, so we can printf */
printf(":%s:%d\n", buf, res);
if (buf[0]=='z') STOP=TRUE;
}
/* restore the old port settings */
tcsetattr(fd,TCSANOW,&oldtio);
}
close(fd); return 0; } |
4.2
4.3
4.4
The given example blocks indefinitely, until input from one of the sources becomes available. If you need to timeout on input, just replace the select call by:
[參考]
1.http://blog.xuite.net/uwlib_mud/twblog/108242774-Linux+RS-232+程式設計
2.https://www.cmrr.umn.edu/~strupp/serial.html.
3.http://www.tldp.org/HOWTO/Serial-Programming-HOWTO/x115.html
Non-Canonical Input Processing
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <stdio.h>
#define BAUDRATE B38400
#define MODEMDEVICE "/dev/ttyS2"
#define _POSIX_SOURCE 1 /* POSIX compliant source */
#define FALSE 0
#define TRUE 1
volatile int STOP=FALSE;
int main(int argc, char *argv[])
{
int fd,c, res;
struct termios oldtio,newtio;
char buf[255];
fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY );
if (fd <0) {perror(MODEMDEVICE); exit(-1); }
tcgetattr(fd,&oldtio); /* save current port settings */
bzero(&newtio, sizeof(newtio));
newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
newtio.c_iflag = IGNPAR;
newtio.c_oflag = 0;
/* set input mode (non-canonical, no echo,...) */
newtio.c_lflag = 0;
newtio.c_cc[VTIME] = 0; /* inter-character timer unused */
newtio.c_cc[VMIN] = 1; /* blocking read until 5 chars received */
tcflush(fd, TCIFLUSH);
tcsetattr(fd,TCSANOW,&newtio);
while (STOP==FALSE) { /* loop for input */
res = read(fd,buf,255); /* returns after 5 chars have been input */
buf[res]=0; /* so we can printf... */
printf(":%s:%d\n", buf, res);
if (buf[0]=='z') STOP=TRUE;
}
tcsetattr(fd,TCSANOW,&oldtio);
close(fd);
return 0; }//main |
4.3
Asynchronous Input
#include <termios.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/signal.h>
#include <sys/types.h>
#define BAUDRATE B38400
#define MODEMDEVICE "/dev/ttyS1"
#define _POSIX_SOURCE 1 /* POSIX compliant source */
#define FALSE 0
#define TRUE 1
volatile int STOP=FALSE;
void signal_handler_IO (int status); /* definition of signal handler */
int wait_flag=TRUE; /* TRUE while no signal received */
int main(int argc, char *argv[])
{
int fd,c, res;
struct termios oldtio,newtio;
struct sigaction saio; /* definition of signal action */
char buf[255];
/* open the device to be non-blocking (read will return immediatly) */
fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY | O_NONBLOCK);
if (fd <0) {perror(MODEMDEVICE); exit(-1); }
/* install the signal handler before making the device asynchronous */
saio.sa_handler = signal_handler_IO;
saio.sa_mask = 0;
saio.sa_flags = 0;
saio.sa_restorer = NULL;
sigaction(SIGIO,&saio,NULL);
/* allow the process to receive SIGIO */
fcntl(fd, F_SETOWN, getpid());
/* Make the file descriptor asynchronous (the manual page says only
O_APPEND and O_NONBLOCK, will work with F_SETFL...) */
fcntl(fd, F_SETFL, FASYNC);
tcgetattr(fd,&oldtio); /* save current port settings */
/* set new port settings for canonical input processing */
newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
newtio.c_iflag = IGNPAR | ICRNL;
newtio.c_oflag = 0;
newtio.c_lflag = ICANON;
newtio.c_cc[VMIN]=1;
newtio.c_cc[VTIME]=0;
tcflush(fd, TCIFLUSH);
tcsetattr(fd,TCSANOW,&newtio);
/* loop while waiting for input. normally we would do something
useful here */
while (STOP==FALSE) {
printf(".\n");usleep(100000);
/* after receiving SIGIO, wait_flag = FALSE, input is available
and can be read */
if (wait_flag==FALSE) {
res = read(fd,buf,255);
buf[res]=0;
printf(":%s:%d\n", buf, res);
if (res==1) STOP=TRUE; /* stop loop if only a CR was input */
wait_flag = TRUE; /* wait for new input */
}
}
/* restore old port settings */
tcsetattr(fd,TCSANOW,&oldtio);
close(fd); return 0;
}
/***************************************************************************
* signal handler. sets wait_flag to FALSE, to indicate above loop that *
* characters have been received. *
***************************************************************************/
void signal_handler_IO (int status)
{
printf("received SIGIO signal.\n");
wait_flag = FALSE;
}
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4.4
Waiting for Input from Multiple Sources
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
int fd1, fd2; /* input sources 1 and 2 */
fd_set readfs; /* file descriptor set */
int maxfd; /* maximum file desciptor used */
int loop=1; /* loop while TRUE */
/* open_input_source opens a device, sets the port correctly, and
returns a file descriptor */
fd1 = open_input_source("/dev/ttyS1"); /* COM2 */
if (fd1<0) exit(0);
fd2 = open_input_source("/dev/ttyS2"); /* COM3 */
if (fd2<0) exit(0);
maxfd = MAX (fd1, fd2)+1; /* maximum bit entry (fd) to test */
/* loop for input */
while (loop) {
FD_SET(fd1, &readfs); /* set testing for source 1 */
FD_SET(fd2, &readfs); /* set testing for source 2 */
/* block until input becomes available */
select(maxfd, &readfs, NULL, NULL, NULL);
if (FD_ISSET(fd1)) /* input from source 1 available */
handle_input_from_source1();
if (FD_ISSET(fd2)) /* input from source 2 available */
handle_input_from_source2();
}
close(fd1); close(fd2); return 0;
}
|
The given example blocks indefinitely, until input from one of the sources becomes available. If you need to timeout on input, just replace the select call by:
int res;
struct timeval Timeout;
/* set timeout value within input loop */
Timeout.tv_usec = 0; /* milliseconds */
Timeout.tv_sec = 1; /* seconds */
res = select(maxfd, &readfs, NULL, NULL, &Timeout);
if (res==0)
/* number of file descriptors with input = 0, timeout occurred. */
|
1.http://blog.xuite.net/uwlib_mud/twblog/108242774-Linux+RS-232+程式設計
2.https://www.cmrr.umn.edu/~strupp/serial.html.
3.http://www.tldp.org/HOWTO/Serial-Programming-HOWTO/x115.html
